1. Field of the Invention
This invention relates to an element utilizing an electrochemical color-forming and color-quenching phenomenon, that is, the electrochromic effect, and more particularly to an elemental device having a novel electrochromic layer, which can form a color, on the anode side.
2. Description of the Prior Art
A conventional electrochromic element has been produced by forming an insulating layer and a coating film as a color-forming layer at the cathode side between a pair of electrode plates. The coating film is made of tungsten dioxide (WO.sub.2), tungsten trioxide (WO.sub.3), molybdenum dioxide (MoO.sub.2), molybdenum trioxide (MoO.sub.3), divanadium pentoxide (V.sub.2 O.sub.5), or the like. Further, it has been proposed to use, as a color-forming layer at the anode side, a coat made of iridium hydroxide (Ir(OH).sub.2), nickel hydroxide (Ni(OH).sub.2), or chromium trioxide (Cr.sub.2 O.sub.3), alone or in combination with the above cathode-side color-forming layer.
These entirely solid electrochromic elements of the prior art generally have the problems of low response speed, poor color-forming effect, particularly low density of color formed, and short service life, and may have still other problems. These problems are significant objections to practical applications of electrochromic elements.